Print hammer mechanism with magnetic reinforcement to cath hammer

ABSTRACT

In a helical line printer having a limited number of type wheels, the type wheels and corresponding hammers are held on a fixed frame while the paper carriage is moved laterally in a repetitive manner by a cam drive such that each type wheel and hammer combination prints out a plurality of characters per line, the paper carriage being returned laterally to its starting position after the printing of a complete line, while the paper is indexed to the next row. The print hammers, normally maintained in a spring loaded position by a permanent magnet, are actuated by energizing a coil to produce a bucking magnetic field which counteracts the field of the permanent magnet, and are caught and locked on rebound from the type wheel by the permanent magnet.

Elnite States Patent Car-gill 51 Dec. 26, 1972 [54] PRINT HAMMER MECHANISM WITH MAGNETIC REINFORCEMENT TO CATH HAMMER [72] Inventor: Norman Allen Cargill, Warminster,

[73] Assignee: Peripheral Dynamics Inc., Norristown, Pa.

[22] Filed: July 13, 1970 [21] Appl. No.: 54,200

[52] US. Cl. ..101/93 C [51] Int. Cl ..B4lj 9/36, B4lj 9/42 [58] Field of Search ..101/93 C, 96, 110; 197/18, 197/19, 49, 50,51, 52,53, 54,55,133

[56] References Cited UNITED STATES PATENTS 3,385,213 5/1968 Stephan ..101/110 3,049,990 8/1962 Brown et al 3,156,180 11/1964 Barnes 3,351,006 11/1967 Belson 3,442,364 5/1969 Ragen 3,356,199 12/1967 Robinson 3,335,659 8/1967 Schacht et a1. ..101/93 C Brown et a1 ..101/93 C Primary Examiner-Robert E. Pulfrey Assistant Examiner-E. M. Coven Attorney-Paul & Paul [57] ABSTRACT In a helical line printer having a limited number of type wheels, the type wheels and corresponding hammers are held on a fixed frame while the paper carriage is moved laterally in a repetitive manner by a cam drive such that each type wheel and-hammer combination prints out a plurality of characters per line, the paper carriage being returned laterally to its starting position after the printing of a complete line, while the paper is indexed to the next row. The print hammers, normally maintained in a spring loaded position by a permanent magnet, are actuated by energizing a coil to produce a bucking magnetic field which counteracts the field of the permanent magnet, and are caught and locked on rebound from the type wheel by the permanent magnet.

4 Claims, 7 Drawing Figures PATENTED 2 6 I97? 3 7 07. l 2 2 sum 1- or 3 INVENTOR. Norman Allen Corgi ll ATTORNEYS.

PATENTEDDEI3261972 snmanrs INVENTOR. Norman Alien Corgill WV/M ATTORN EYS.

PATENTED M112 m2 SHEET 3 [IF 3 CARRIAGE POSITION Fig. 7

INVENTOR. Norman Allen Corgill BY W+M ATTOR N EYS PRINT HAMMER MECHANISM WITH MAGNETIC REINFORCEMENT TO CATH HAMMER BACKGROUND OF THE INVENTION 1. Field of the Invention This invention lies in the field of helical wheel line printers and, more particularly, limited wheel printers having the paper carriage driven repetitively with Art Helical wheel type line printers are well known in the art. In the basic single helical wheel line printer, as disclosed in U. S. Pat. No. 2,843,243, the helical wheel and hammer are moved synchronously across the entire line of print, the hammer being actuated corresponding to each desired column of print across the line. At the end ofa line of print, both the helical wheel and the hammer are returned to the starting position for the next line, while the paper is shifted into position to receive the print of the next line. An adaptation of this original type of line printer is the limited wheel printer, comprising a limited number of wheels, each of which wheels advances through a given pitch or distance, each wheel having an associated hammer which moves in conjunction with it and which is actuated corresponding to each desired print character.

While, for a given wheel rotation speed, the limited wheel line printer inherently operates at a lower net print out speed, it provides the basic advantage of lower cost due to having to incorporate only a limited number of wheel-hammer pairs. There is thus a direct trade-off between printer speed and cost. In the limited wheel line printer it is, of course, necessary to synchronize the movement of each helical wheel and its associated hammer. A number of methods are devised and are in practice for accomplishing this. However, moving the print wheels and the hammers synchronously requires building a frame which supports both, which frame itself must be moved within the overall printer frame. It is thus necessary to move, and move precisely, a large frame which carries considerable weight. In addition to the engineering required to efficiently and precisely move the frame carrying the type wheels and hammers, it requires considerable power, and consequent expense, to drive such a heavy frame. It is therefore desirable to mount the print wheels and hammers on a fixed frame and provide relative movement of the paper by another means.

In conventional line printers, the hammers are actuated through electromagnets which impart a driving force to the hammer, driving it against the print wheel, this driving force acting against a spring mechanism which returns the drive hammer to a normal unbiased position. Thus, the energy which must be supplied by the electromagnet is not only that required to drive the hammer against the print wheel, but also that amount of energy necessary to work against the spring. Thus, the conventional line printer operates with inefficiencies both in the manner of positioning the print wheels and in driving the hammers against the wheels.

SUMMARY OF THE INVENTION It is an object of this invention to provide a limited wheel line printer having helical print wheels and corresponding hammers mounted in fixed positions relative to the frame of the printer, and means for driving respect to the type wheels. 2. Description of the Prior m the paper carriage cyclically with respect to the position of the hammers and wheels, so as to overcome the disadvantages of the prior art methods of moving the hammers and wheels with respect to the fixed position paper carriage.

It is a further object of this invention to provide a limited line printer with means for actuating the print hammers in a manner which overcomes the inefficiencies of the prior art.

It is a further object of this invention to provide limited line printers having a more efficient manner of providing relative lateral motion of the print wheels with respect to the paper, and providing a more efficient manner of actuating the print hammers.

Accordingly, the invention provides a limited wheel line printer comprising a main printer frame, a limited number of fixed position type wheels arranged longitudinally on a common axis, hammers corresponding respectively to each type wheel and also held in fixed positions such that the spacial relationship between each wheel and its respective hammer is unchanged during operation of the printer, a paper carriage moveably mounted on said main frame and driven laterally in a repetitive manner by a cam drive a distance corresponding to the separation of adjacent type wheels, the paper carriage being returned laterally to its starting position each time a line is printed and the paper is indexed to the next row. The fixed position print hammers are normally maintained in a spring loaded position by a permanent magnet and released by application of an opposing magnetic field. The hammers are caught and locked by the attractive force of the permanent magnet on the first rebound from the type wheel, and, in an alternate embodiment, are reloaded by an additive magnetic field timed to catch and lock the hammer.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of the line printer.

FIG. 2 is a sectional view taken along lines 2-2.

FIGO 3 is a plan view taken along lines 33.

FIG. 4 is a schematic diagram of the bifilar coil windmg.

FIG. 5 is a sectional view of an alternate embodiment of the hammer and hammer actuator.

FIG. 6 is a partial view showing pairs of print wheels having opposite helixes.

FIG. 7 is a graph showing movement of the paper carriage in the embodiment using print wheel pairs.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1 of the drawings, side frames 51 constitute a portion of the main housing of the line printer. Mounted on one of side frames 51 is a motor which provides the moving force for the printer. Motor 50 is connected through a series of belts 52 to a cam shaft 54, a paper tractor shaft 91, and a type wheel shaft 65.

Type wheel shaft has mounted thereon a plurality of type wheels 66, adjacent wheels being separated by spacers 67. The type wheels are fixedly attached to shaft 65, and are rotated about shaft 65. Each type wheel has alphanumeric characters fixed thereon in a typical helical arrangement. It is to be noted that shaft 65 is mounted within the two side frames shown, and can only rotate about its axis, there being no provision for imparting lateral movement to the type wheel shaft.

In fixed relation to each type wheel 66 is a hammer 75, shown in more detail in FIG. 2. The hammers 75 are also mounted in fixed positions, such that each hammer is held stationary with respect to its respective type wheel.

Still referring to FIG. 1, belt 52 drives cam shaft 54 which is connected to cam 55. Held firmly seated against the track portion of cam 55 is a cam follower 56 which is integrally connected to a carriage support shaft 57. The carriage support shaft, which carries the paper carriage, not shown, and thus the paper on which the printout is made, is held firmly against the cam by springs 58, and rides in a back and forth or lateral manner in accordance with .the cam configuration. As is seen more clearly in FIG. 3, the angular rotation of cam 55 causes cam follower 56, and the carriage shaft 57, to move laterally in a reciprocating manner, this providing relative motion of the paper carriage with respect to the fixed type wheels and fixed position hammers.

Also mounted on the frame sides 51, and driven by pulleys 52, is paper tractor shaft 91, which drives paper tractors 90, which impart line-to-line motion to the paper carried by the paper carriage. The paper tractor shaft 91 is driven by a conventional clutch 92 operated upon electrical signals supplied to a solenoid 93. The paper tractors 90 are supported by carriage shaft 57, and move freely in a lateral direction with respect to shaft 91. I

Referring now to FIG. 2, the relationship of the type wheels, the hammers, and the paper on which the printout is achieved may be seen. Hammer 75 has a head 76, which is driven forward and against the type wheel 66, and an armature 77, suitably made of soft steel. The armature 77 extends through an opening in pole piece 79 to which is attached a permanent magnet 80. A center pole 82, also suitably made of soft steel, is attached to pole 79 and located at the rear of the same opening, and is adjustable in position by rotation of the threaded end 83. Under normal operating conditions, the magnetic field established by permanent magnet 80 passes through poles 79 and 82, and pulls armature 77 into the opening, thus holding it in a loaded, or cocked condition, with head 76 displaced from type wheel 66. The magnetic field provides a force opposing the spring force exerted by pring 81, which spring would drive the hammer against the type wheel in the absence of the restraining magnetic field. In the normal loaded position, armature 77 is flush against center pole 82, providing a continuous path for the magnetic field created by the magnet.

Also attached to pole pieces 79 is a coil 85 which, when energized with a DC current, provides a magnetic field through center pole piece 82. Depending upon the manner of energizing the coil, such magnetic field is either opposing, or bucking, that of the permanent magnet, or is in such a direction as to reinforce it. FIG. 4 shows a suitable bifilar configuration for providing alternately an opposing or reinforcing field. The bifilar coil is separated into two components, and by the application of a single DC voltage across either terminal, a magnetic field of opposing or reinforcing polarity is obtained.

In operation, an opposing current is applied to coil 85 coincident with the moment that the desired character on the helical wheel passes opposite the hammer head. The strength of the opposing magnetic field is sufficient to overcome the restraining force of the permanent magnet, thus releasing the hammer which is drivenforward by spring 81. It is to be noted that the unrestrained hammer responds in a simple harmonic manner, the hammer having a maximum momentum at the moment that springs 81 pass through their straight condition. The position of spring 81 with respect to the type wheel 66 is such that the springs are appreciably straight at the moment that the tip of hammer 76 makes contact, through the paper 99, with the type wheel 66. Thus, the arrangement as shown in FIG. 2 provides an optimally efficient manner of driving the hammer and of delivering maximum hammer energy, as contrasted to the conventional design where a hammer is driven against a spring.

The hammer in combination with the spring 81 has a natural frequency of oscillation, resulting in a specific time period between time of release of the hammer and the time that it achieves its greatest return upon bouncing off of the type wheel. At exactly such time, the coil 85 is again pulsed with a DC current, this time pulsing the second winding so as to produce a magnetic field which reinforces the magnetic field created by the magnet 80. In such manner, minimum electrical power is required to catch and hold the hammer in a locked condition. Further, by the use of this mechanism the hammer bounces off of type wheel 66 only once, thus eliminating the usual smudging that occurs when the hammer bounces off the type wheel several times or is allowed to come to rest against the type wheel for a limited period of time. It is to be noted that the circuit for providing alternating polarity electromagnetic pulses may be varied, and the invention is not limited to the bifilar winding as shown.

An alternate embodiment of the actuator, not requir-. ing the second current pulse, is shown in FIG. 5. In this embodiment, the permanent magnet 101 is made of sufficient strength that the hammer is self-latching after the first, or bucking, DC current pulse is removed. Upon release of the hammer, it travels a distance of approximately 0.060 inch before striking the type wheel. By designing the permanent magnet 101 and the magnetic circuit such that the magnet can pull the hammer across at least a 0.060 inch gap, the hammer will be reloaded after the bucking DC pulse, applied to coil 102, terminates. Magnetic circuit pieces 103 and 104, preferably constructed of soft iron, provide the magnetic circuit path. Piece 104 is constructed to surround hammer armature 106, so as to maximize the flux acting on the armature.

In operation of the line printer of this invention, the movement of paper carriage 57 is determined by the configuration of cam 55. As shown in FIG. 3, cam 55 is in a zero, or starting position, corresponding to which the paper carriage is in position for start of the printing of a line. As the cam is rotated, cam follower 56 and carriage shaft 57 are driven to the left, as indicated in FIG, 3, providing relative displacement of the paper with respect to the fixed position type wheels. The cam surface is such that the lateral advance on the shaft 57 is linear with respect to time, the paper moving linearly for a distance equal to the spacing, or pitch between adjacent type wheels. By way of illustration, the line printer of this invention may utilize 16 helical type wheels, with a spacing between adjacent wheels such that each wheel covers eight spaces during the printing of a line. Thus, while the cam is linearly moving the paper carriage shaft with respect to the wheels, each wheel is rotated 8 times, with a corresponding character printout for each wheel rotation, depending upon the signal information transmitted to the respective hammer actuators. Thus, after the cam has driven the paper carriage eight spaces with respect to the type wheels, the 16 wheel printer has printed out a line comprised of 128 characters, or columns. correspondingly, the total pitch of the cam is equal to eight column spaces.

For a typical helical wheel having a pitch of 0.1 inch, with each helical wheel printing eight columns, the cam produces an 0.8 inch range in movement of the paper carriage. It is noted that the movement of the cam is synchronized with that of the type wheels, which are constantly rotating, it being important to maintain synchronization between the angular rotation of the type wheels and the linear movement of the paper. After a complete line has been printed, and during the time that the paper tractor is shifting the paper to the next line, it is necessary to return the paper carriage to the starting position. This is accomplished by further rotation of the cam, during which time the cam follower returns to the starting position as shown in FIG. 3. It has been found that a suitable cam design is that which advances the paper carriage linearly for about two-thirds of the cam rotation, and returns the paper carriage during the last third of the cam rotation, such that the return time is approximately one-halfthe paper advance time.

At the moment the carriage shaft 57 begins to advance from its starting, or zero displacement position, each type wheel passes through its zero angular displacement position. During the first revolution of the type wheel, during which time the paper carriage advances one space, the hammer is actuated by a DC current signal applied to a first winding of bifilar coil 85. This signal is synchronized with the angular rotation of the type wheel, such that the hammer is released opposite the desired character. The DC current signal is of short duration, a signal of less than 1 millisecond being sufficient to release the hammer. The natural frequency of oscillation of the hammer, determined by the length of spring 81 and the mass of hammer 75, produces a typical oscillation period of approximately 5 milliseconds. Accordingly, a second DC pulse is applied to the second winding of the bifilar coil approximately 5 milliseconds after the first pulse, the second pulse generating a magnetic field reinforcing the magnetic field of the permanent magnet, thereby catching and locking the hammer after its first bounce off the type wheel. During the next revolution of the type wheel, the same procedure is followed. In this manner, the type wheel is actuated eight times during the lateral movement of the paper carriage through eight column spaces. During the return of the paper carriage to its zero displacement position, the type wheels are rotated an integral number of revolutions, such that each type wheel passes through its zero angular displacement position at exactly the same time that the paper carriage passes through its zero displacement position.

In an alternate embodiment of this invention, helical wheel pairs, as illustrated in FIG. 6, are utilized. For each pair of wheels, one wheel has a forward helix and the other a backward helix, with each wheel having a corresponding hammer. Accordingly, the cam is designed to move the carriage in the forward and reverse directions at equal speeds, with turn-around periods during which the paper is shifted to the next line. Referring to FIG. 7, movement of the paper carriage with time is shown. From time A to time B the paper carriage is advanced linearly to the left, while the forward F helical wheels are used. Between times B and C, the carriage is moved further to the left and back to the right, such that at time C it is in the same position as at time B, but advancing linearly to the right. During this turn-around time, the paper is advanced for the printing of the next line. From time C to time D, the paper carriage is advanced linearly to the right, during which time the reverse R wheels are used. Thus, the carriage return time is utilized for printing and an overall time savings is achieved, thereby providing an increase in speed of the printer.

It is appreciated that other combinations may be adapted for use with this invention. The illustrations are given solely to explain the operation of the printer of this invention, and do not limit the invention as claimed.

I claim:

1. In a line printer having a plurality of print wheels, hammer apparatus comprising a plurality of hammers, each hammer being pivotably mounted in a fixed position relative to a respective print wheel, and each said hammer comprising:

a. a hammer head having an armature made of a magnetic conducting material connected thereto;

b. a pole piece positioned adjacent said armature and adapted to hold said armature in contact therewith when a magnetic field is established therein;

0. magnetic field means connected to said pole piece for establishing a continuous magnetic field therein of sufficient strength to hold said armature in contact with said pole piece;

d. a hammer drive spring connected to said hammer head to provide a spring force opposing the holding force of said continuous magnetic field;

e. a coil mounted about said pole piece and having a first winding adapted to generate a first magnetic field opposing said continuous magnetic field, and a second winding to generate a second magnetic field reinforcing said continuous magnetic field; and,

f. first actuating means for actuating said first coil and generating said first magnetic field with a magnitude which substantially cancels out said continuous magnetic field, and for a first duration such that said spring force is substantially unopposed long enough to release said hammer such that it is driven against said respective type wheel, said duration being ended prior to the rebound of said hammer from said type wheel, and second actuating means for actuating said second coil and generating said second magnetic field with a magnitude sufficient to catch and lock said hammer on its rebound from said type wheel and, for a second duration initiated at the time of such rebound and terminated prior to the next release of said hammer.

The apparatus as described in claim 1 wherein said spring by a continuous magnetic force only;

b. releasing said hammer by generating a first magnetic force opposing said continuous magnetic force and of a magnitude to substantially cancel said continuous magnetic force, and for a first duration limited such that said first magnetic force is terminated prior to the time said released hammer rebounds after striking said type wheel;

. driving said released hammer against said type wheel by the force of said drive spring; and

. catching and holding said driven hammer after its first rebound off of said type wheel by generating a second magnetic force of sufficient magnitude and in a direction so as to reinforce said continuous magnetic force, said second magnetic force having a duration commencing after said hammer strikes said-type wheel and terminating after said hammer is caught and held and before the next release of said hammer, said hammer being held against said drive spring by said continuous magnetic force only until the generation of said next opposing magnetic force.

UNITED STATES PATENT ()FNCE QERTINCATE GEE QGRRIECTEON Patent No. 07,122 Dated December 26,1972

Inventor s Norman Allen Cargill It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the Title, on Title page and at column 1, CATH should be CATCH Column 3, line 50 pring should be -s pring.

Column 4, line 65, after "advance" -onshould be of-.

.Signed and sealed this 22nd day of May 1973.

(SEAL) Atte'st:

EDWARD M.FLETCHER,JR. ROBERT'GOTTSCHALK Attesting Officer Commissioner of Patents FORM PO-105O (10-69) USCOMM-DC 6037 G-P GQ 

1. In a line printer having a plurality of print wheels, hammer apparatus comprising a plurality of hammers, each hammer being pivotably mounted in a fixed position relative to a respective print wheel, and each said hammer cOmprising: a. a hammer head having an armature made of a magnetic conducting material connected thereto; b. a pole piece positioned adjacent said armature and adapted to hold said armature in contact therewith when a magnetic field is established therein; c. magnetic field means connected to said pole piece for establishing a continuous magnetic field therein of sufficient strength to hold said armature in contact with said pole piece; d. a hammer drive spring connected to said hammer head to provide a spring force opposing the holding force of said continuous magnetic field; e. a coil mounted about said pole piece and having a first winding adapted to generate a first magnetic field opposing said continuous magnetic field, and a second winding to generate a second magnetic field reinforcing said continuous magnetic field; and, f. first actuating means for actuating said first coil and generating said first magnetic field with a magnitude which substantially cancels out said continuous magnetic field, and for a first duration such that said spring force is substantially unopposed long enough to release said hammer such that it is driven against said respective type wheel, said duration being ended prior to the rebound of said hammer from said type wheel, and second actuating means for actuating said second coil and generating said second magnetic field with a magnitude sufficient to catch and lock said hammer on its rebound from said type wheel and, for a second duration initiated at the time of such rebound and terminated prior to the next release of said hammer.
 2. The apparatus as described in claim 1 wherein said coil has a bifilar winding.
 3. The line printer as described in claim 1 wherein said pole piece comprises a contact element adjustable in position, said armature being normally held in contact with said contact element.
 4. In a line printer having a hammer acting in combination with a type wheel, the method of actuating said hammer so that it strikes said type wheel only once, comprising: a. normally holding said hammer against a drive spring by a continuous magnetic force only; b. releasing said hammer by generating a first magnetic force opposing said continuous magnetic force and of a magnitude to substantially cancel said continuous magnetic force, and for a first duration limited such that said first magnetic force is terminated prior to the time said released hammer rebounds after striking said type wheel; c. driving said released hammer against said type wheel by the force of said drive spring; and d. catching and holding said driven hammer after its first rebound off of said type wheel by generating a second magnetic force of sufficient magnitude and in a direction so as to reinforce said continuous magnetic force, said second magnetic force having a duration commencing after said hammer strikes said type wheel and terminating after said hammer is caught and held and before the next release of said hammer, said hammer being held against said drive spring by said continuous magnetic force only until the generation of said next opposing magnetic force. 